Internal combustion engine

ABSTRACT

An internal combustion engine according to this invention is provided with intake ports each of which is formed to guide a flow of inducted air in a particular direction. Each intake port includes, in the vicinity of its corresponding intake opening to a combustion chamber, a bent port portion bent at a greater curvature than a port portion on a side upstream of the bent port portion. The bent port portion has a greater inner diameter than the inner diameter of the corresponding intake opening, whereby air can be inducted in a sufficient amount without deterioration to the directing function for air to be inducted into the combustion chamber.

BACKGROUND OF THE INVENTION

1) Field of the Invention

This invention relates to an internal combustion engine provided withone or more intake ports per cylinder, each of said intake ports beingcapable of directing a flow of air to be inducted to a combustionchamber, and especially, to an internal combustion engine suitable foruse as a stratified burning internal combustion engine in which one ormore tumble flows are formed from the so-directed flow or flows ofinducted air inside the combustion chamber.

2) Description of the Related Art

With an objective toward improving combustion characteristics in acombustion chamber, there are known internal combustion engines in whichthe configuration of each intake port is designed to direct a flow ofair to be inducted into the combustion chamber.

Stratified burning internal combustion engines are also known. To permitoperation at low fuel consumption, a layer of a rich air-fuel mixture isformed in a combustion chamber and this fuel-rich layer is ignited. Thismakes it possible to ignite an air-fuel mixture having a large air/fuelratio as a whole. As a method for forming the layer of the rich air-fuelmixture in the combustion chamber, it is known to direct by intake portsflows of air to be inducted into the combustion chamber so thatstratified swirls can be formed inside the combustion chamber. As oneexample of such stratified burning internal combustion engines, astratified burning internal combustion engine in which stratifiedvertical tumble flows, that is, vertical vortices (hereinafter simplyreferred to as "tumble flows") are formed has already beencommercialized as illustrated in FIGS. 37 and 38.

FIGS. 37 and 38 show the structure of one of cylinders of a2-intake-port internal combustion engine, in which there are illustrateda cylinder block 322, a cylinder 324, a piston 326, a cylinder head 328and a combustion chamber 330. Designated at numeral 334 is an upper wallof the combustion chamber 330. The upper wall 334 is shaped in the formof a pentroof which has inclined walls 334a,334b. Intake ports 340,342are open through the inclined wall 334a of the combustion chamber 330and are each provided with an intake valve 358. Incidentally, numeral347 indicates an exhaust port arranged in communication with an exhaustpassage 360, while numeral 359 designates an exhaust valve.

Intake air, which has flowed into the combustion chamber 330 through therespective intake ports 340,342, then flows along the inclined wall 334btoward an inner wall of the cylinder 324, said inner wall being locatedon extensions of axes of the individual intake ports 340,342, wherebytumble flows are formed in the combustion chamber 330 as indicated byarrows Fa,Fm.

As is depicted in FIG. 37, only one of the intake ports, namely, theintake port 342 is provided with an injector 312. A spark plug 310 isarranged adjacent to the intake valve 358 in the intake port 342 whichis provided with the injector 312. In the vicinity of the spark plug310, there is accordingly formed the tumble flow Fm of an air-fuelmixture which has been formed of inducted air and fuel injected from theinjector 312, so that stratified tumble flows consisting of the tumbleflow Fm of the air-fuel mixture and the tumble flow Fa of air are formedin the combustion chamber 330.

Even when the ratio of the air to the fuel inside the combustion chamber330 is high, in other words, even upon lean burn in which the fuelconcentration is low as a whole inside the combustion chamber 330,stable combustion is still feasible owing to the existence of anair-fuel mixture richer in fuel than those present at places remote fromthe spark plug 310, around the spark plug 310.

To direct the flows of air, which are to be introduced into thecombustion chamber 300 through the intake ports 340,342, so that thetumble flows Fa,Fm can be formed in the combustion chamber 330, eachintake port has a substantially straight configuration close to thecombustion chamber 330. As the configuration of a port portion includedin each intake port to perform the above-mentioned directing function, abent configuration having an extremely small curvature can becontemplated in addition to a straight configuration. Whateverconfiguration is adopted for such a directing port portion, both theintake ports 340,342 have to be bent at a curvature, which is thegreatest along the entire lengths of the intake ports 340,342, in thevicinity of the combustion chamber 330. For the flows of air inductedtherethrough, the cross-sectional flow areas are reduced at the bentportions, resulting in such inconvenience that tumble flows cannot beobtained as desired and/or a maximum intake air quantity cannot beachieved to a desired level.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an internal combustionengine which can obtain a sufficient intake air quantity withoutdeterioration to the function to direct flow(s) of inducted air into acombustion chamber.

Another object of the present invention is to provide an internalcombustion engine which can form stronger tumble flow(s) inside acombustion chamber.

A further object of the present invention is to provide an internalcombustion engine which can form stratified tumble flows, including atleast one tumble flow of a rich air-fuel mixture and at least one tumbleflow of a lean air-fuel mixture, in a more complete stratified forminside a combustion chamber.

In one aspect of the present invention, there is thus provided aninternal combustion engine comprising:

a combustion chamber defined by an inner wall of a cylinder, a top wallof a piston fitted in the cylinder and a lower wall of a cylinder head,and

an intake port disposed in the lower wall of the cylinder head andhaving an intake opening selectively opened or closed by an intakevalve, said intake port having in the vicinity of the intake opening abent port portion bent at a greater curvature than a port portion on aside upstream of the curved port portion,

wherein the bent port portion in the vicinity of the intake opening isprovided with an inflated part having a larger inner diameter than theinner wall of the intake opening.

Preferably, the intake opening of the intake port is arranged on oneside of an imaginary plane containing an axis of the cylinder, theintake port has a substantially straight port portion on the sideupstream of the bent port portion for directing an intake air flow sothat inducted air flows from the intake opening toward an opposite sideof the imaginary plane, whereby a tumble flow is formed in thecombustion chamber.

The intake port can have a substantially greater width in an upperportion thereof than in a lower portion thereof in a cross-section takenat a right angle relative to flow lines of air inducted through theintake port so that a central axis of a flow of the air inducted throughthe intake port is offset toward the upper portion. Desirably, theinflated part has been formed by further widening the upper portion inthe bent port portion of the intake port. The intake port can have aninverted, substantially triangular configuration in a cross-sectiontaken at a right angle relative to flow lines of air inducted throughthe intake port.

In another aspect of the present invention, there is also provided aninternal combustion engine comprising:

a combustion chamber defined by an inner wall of a cylinder, a top wallof a piston fitted in the cylinder and a lower wall of a cylinder head,

plural intake ports disposed in the cylinder head on one side of animaginary plane, which contains an axis of the cylinder, and havingintake openings selectively opened or closed by corresponding intakevalves, respectively, whereby air inducted through the intake ports flowfrom the intake openings toward an opposite side of the imaginary planealong the lower wall of the cylinder head to form mutually-paralleltumble flows in the same direction within substantially the entirety ofthe combustion chamber,

a spark plug disposed on an inner wall of the combustion chamber at aposition corresponding to a flow of air inducted through one of theintake ports, and

fuel feed means for feeding fuel into said one of the intake ports, saidone intake port corresponding to the position of the spark plug, wherebystratified tumble flows are formed in the combustion chamber during anintake stroke,

wherein each of the plural intake ports has a guide port portion fordirecting intake air to be inducted into the combustion chamber and abent port portion connecting a downstream end of the guide port portionand the corresponding intake opening, and the bent port portion isprovided with an inflated part having a larger inner diameter than theinner wall of the corresponding intake opening.

Preferably, each intake port has a substantially greater width in anupper portion thereof than in a lower portion thereof in a cross-sectiontaken at a right angle relative to flow lines of air inducted throughthe intake port so that a central axis of a flow of the air inductedthrough the intake port is offset toward the upper portion.

The inflated part can have been formed by further widening the upperportion in the bent port portion of the intake port. Desirably, eachintake port has an inverted, substantially triangular configuration in across-section taken at a right angle relative to flow lines of airinducted through the intake port.

In a further aspect of the present invention, there is also provided aninternal combustion engine comprising:

a combustion chamber defined by an inner wall of a cylinder, a top wallof a piston fitted in the cylinder and a lower wall of a cylinder head,

two intake ports disposed in the cylinder head on one side of animaginary plane, which contains an axis of the cylinder, and havingintake openings selectively opened or closed by corresponding intakevalves, respectively, whereby air inducted through the intake ports flowfrom the intake openings toward an opposite side of the imaginary planealong the lower wall of the cylinder head to form mutually-paralleltumble flows in the same direction within substantially the entirety ofthe combustion chamber,

a longitudinal partition dividing at least one of the intake ports intoplural passages,

a spark plug disposed on an inner wall of the combustion chamber at aposition corresponding to at least one of the passages, and

fuel feed means for feeding fuel into said at least one intake port,said at least one intake port corresponding to the position of the sparkplug, whereby stratified tumble flows are formed in the combustionchamber during an intake stroke,

wherein each of the two intake ports has a guide port portion fordirecting intake air to be inducted into the combustion chamber and abent port portion connecting a downstream end of the guide port portionand the corresponding intake opening, and the bent port portion isprovided with an inflated part having a larger inner diameter than theinner wall of the corresponding intake opening.

Preferably, each intake port has a substantially greater width in anupper portion thereof than in a lower portion thereof in a cross-sectiontaken at a right angle relative to flow lines of air inducted throughthe intake port so that a central axis of a flow of the air inductedthrough the intake port is offset toward the upper portion. The inflatedpart has been formed by further widening the upper portion in the bentport portion of the intake port. Each intake port can have an inverted,substantially triangular configuration in a cross-section taken at aright angle relative to flow lines of air inducted through the intakeport.

The present invention can therefore achieve its objects described above.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will become apparent from the following description and theappended claims, taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 is a schematic perspective view of a stratified burning internalcombustion engine according to a first embodiment of the presentinvention;

FIG. 2 is a schematic fragmentary top plan view of intake ports of thestratified burning internal combustion engine according to the firstembodiment of the present invention as viewed in the direction of arrowA in FIG. 1;

FIG. 3 is a schematic fragmentary side view of a combustion chamber ofthe stratified burning internal combustion engine according to the firstembodiment of the present invention as viewed in the direction of arrowA' in FIG. 1;

FIG. 4(a) is a schematic fragmentary perspective view of a piston of thestratified burning internal combustion engine according to the firstembodiment of the present invention and FIG. 4(b) is a fragmentarycross-sectional view of the piston, and FIGS. 4(a) and 4(b) illustratein detail the configuration of a top wall of the piston;

FIG. 5 is a schematic fragmentary cross-sectional view of one of theintake ports of the stratified burning internal combustion engineaccording to the first embodiment of the present invention, taken in thedirection of arrows C--C of FIG. 2;

FIG. 6 is a schematic top plan view of the combustion chamber of thestratified burning internal combustion engine according to the firstembodiment of the present invention as viewed in the direction of arrowA in FIG. 1;

FIG. 7 is a schematic fragmentary cross-sectional view of one of theintake ports of the stratified burning internal combustion engineaccording to the first embodiment of the present invention as viewed inthe direction of arrows C--C in FIG. 2, in which an associated partitionhas been omitted.

FIGS. 8(a) through 8(g) are schematic cross-sectional views of one ofthe intake ports of the stratified burning internal combustion engineaccording to the first embodiment of the present invention, andcorrespond to sections 8(a)-8(a) to 8(g)-8(g) in FIG. 7, respectively;

FIG. 9 is a schematic cross-sectional view of one of the intake ports ofthe stratified burning internal combustion engine according to the firstembodiment of the present invention, taken in the direction of arrowsIX--IX of FIG. 5;

FIG. 10 diagrammatically shows effects of the structure of the intakeports of the stratified burning internal combustion engine according tothe first embodiment of the present invention;

FIG. 11 also diagrammatically illustrates effects of the structure ofthe stratified burning internal combustion engine according to the firstembodiment of the present invention;

FIG. 12 also diagrammatically depicts effects of the structure of thestratified burning internal combustion engine according to the firstembodiment of the present invention;

FIG. 13 also diagrammatically shows effects of the structure of thestratified burning internal combustion engine according to the firstembodiment of the present invention;

FIGS. 14(a) and 14(b) are similar to FIGS. 4(a) and 4(b), respectively,and illustrate in detail the configuration of a top wall of amodification of the piston;

FIGS. 15(a) and 15(b) are similar to FIGS. 4(a) and 4(b), respectively,and depict in detail the configuration of a top wall of a furthermodification of the piston;

FIG. 16 diagrammatically shows effects of the configuration of the topwall of the piston of the stratified burning internal combustion engineaccording to the first embodiment of the present invention;

FIG. 17 is similar to FIG. 5 and illustrates the structure of amodification of each intake port of the stratified burning internalcombustion engine according to the first embodiment of the presentinvention;

FIG. 18 is similar to FIG. 1 and illustrates a modification of thestratified burning internal combustion engine according to the firstembodiment of the present invention;

FIG. 19 is similar to FIG. 5 and illustrates the structure of eachintake port of the modification shown in FIG. 18;

FIG. 20 is a schematic fragmentary cross-sectional view of amodification of the intake port depicted in FIG. 19;

FIG. 21 is a schematic fragmentary cross-sectional view of amodification of the intake port shown in FIG. 20;

FIG. 22 is a schematic fragmentary transverse cross-sectional view ofthe intake port shown in FIG. 21, taken in the direction of arrowsXXII--XXII of FIG. 21;

FIG. 23 is similar to FIG. 1 and illustrates a further modification ofthe stratified burning internal combustion engine according to the firstembodiment of the present invention;

FIG. 24 is a schematic fragmentary cross-sectional view of each intakeport of the further modification, taken in the direction of arrowsXXIV--XXIV of FIG. 23;

FIG. 25 is a schematic fragmentary transverse cross-sectional view of afurther modification of the intake port shown in FIG. 23, taken in thedirection of arrows XXV--XXV of FIG. 23;

FIGS. 26(a) through 26(d) schematically illustrate various types of fuelinjections in each intake port;

FIG. 27 is a schematic top plan view of a modification of a partition ineach intake port useful in the practice of the present invention;

FIG. 28 is a schematic top plan view of a further modification of thepartition of FIG. 27;

FIG. 29 is a schematic top plan view of a still further modification ofthe partition of FIG. 27;

FIG. 30 is a schematic top plan view of a still further modification ofthe partition of FIG. 27;

FIG. 31 is a schematic view of an intake passage useful in the practiceof the present invention, and illustrates a modification of the intakepassage of FIG. 7;

FIGS. 32(a) through 32(g) are schematic cross-sectional views of theintake passage of FIG. 31, and correspond to 32(a)-32(a) to 32(g)-32(g)cross-sections in FIG. 31, respectively;

FIG. 33 is similar to FIG. 32(c) and illustrates a further modificationof the intake passage of FIG. 31;

FIG. 34 is a schematic perspective view of the stratified burninginternal combustion engine according to the second embodiment of thepresent invention, in which intake ports having no partition have beenincorporated;

FIG. 35 is a schematic transverse cross-sectional view of the intakeports, taken in the direction of arrows XXXV--XXXV on FIG. 34;

FIG. 36 is a schematic top plan view of the stratified burning internalcombustion engine of FIG. 34;

FIG. 37 is a schematic perspective view of a conventional stratifiedburning internal combustion engine; and

FIG. 38 is a schematic cross-sectional view of the conventionalstratified burning internal combustion engine of FIG. 37.

DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS

The first embodiment of the present invention is now described withreference to FIG. 1 through FIG. 13.

Referring first to FIG. 1, the outline construction of the stratifiedburning internal combustion engine according to the first embodimentwill be described. In each cylinder of the internal combustion engine, acombustion chamber 30 is defined surrounded by an inner wall of acylinder 24 formed in a cylinder block 22, a piston 26 and a cylinderhead 28. An intake port 46 is provided in communication with thecombustion chamber 30. Described in detail, this intake port 46 isdivided into two sections by a bifurcation 46C so that the intake port46 is in the form of a Siamese port having two intake ports 46A,46Bwhich penetrate into the combustion chamber 30. At each of intakeopenings through which the intake ports 46A,46B penetrate into thecombustion chamber 30, respectively, an intake valve 58 is disposed toselectively open or close the corresponding intake port. Further, anexhaust port 47 is also provided in communication with the combustionchamber 30. Described specifically, the exhaust port 47 is divided at alongitudinal intermediary point thereof into two sections, whereby theexhaust port 47 is in the form of a Siamese port having two exhaustports 47A,47B which penetrate into the combustion chamber 30. At anopening of each exhaust port to the combustion chamber 30, an exhaustvalve 61 (see FIG. 3) is disposed. Incidentally, the intake ports46A,46B penetrate into the combustion chamber 30 on one side of animaginary plane FC which contains an axis L of the cylinder block 22,while the exhaust ports 47A,47B penetrate into the combustion chamber 30on an opposite side of the imaginary plane FC. A ceiling of thecombustion chamber 30, said ceiling being defined by a lower wall 60 ofthe cylinder head 28, is shaped in the form of a pentroof having twoinclined walls 60a,60b (see FIG. 3) arranged in such a way that a top ofthe ceiling is located on the imaginary plane FC. In addition, a sparkplug 11 as an ignition means is disposed substantially centrally in theceiling of the combustion chamber 30.

Arranged at a point upstream of the bifurcation 46C in the intake port46 is an injector 12 as a fuel injection means which will be describedin detail herein. Through the injector 12, fuel is injected toward adownstream side approximately from the bifurcation 46C in the intakeport 46. Axes 1A,1B of the respective intake ports 46A,46B extend asmutually-parallel, straight lines as shown in FIGS. 1 and 2. Theindividual intake ports 46A,46B therefore include directing straightguide portions which extend in parallel with each other. Air flowsinducted through the respective intake ports 46A,46B are hence allowedto flow as mutually-parallel flows into the combustion chamber 30. Theair, which have been inducted through each intake port 46A or 46B andhas flowed into the combustion chamber 30 during an intake stroke, flowstoward the opposite side of the imaginary plane FC along the inclinedwall 60b of the lower wall 60 of the cylinder head 28 which forms theceiling of the combustion chamber 30. The inducted air then descendsalong the inner wall of the cylinder 24 onto a top wall 35 of the piston26, and further ascends along the inner wall of the cylinder 24 onto theinclined wall 60a of the lower wall 60 of the cylinder head 28. As aresult, vertical vortices (tumble flows) are formed within substantiallythe entirety of the combustion chamber 30.

The intake ports 46A,46B are provided with partitions 21,21,respectively. These partitions 21,21 vertically extend along the axes1A,1B, respectively. Each partition 21 divides the associated intakeport 46A or 46B into a central passage 4 and a side passage 5 which lieson an outer side of the central passage 4. The injector 12 is arrangedto inject fuel toward the central passage 4 which serves to form atumble flow at a position corresponding to the spark plug 11.

Owing to the construction described above, a fuel-containing tumble flowFm and a fuel-free tumble flow Fa are formed in layers in the combustionchamber 30 during an intake stroke. It is important that these tumbleflows Fm and Fa are substantially parallel with each other and move inthe same direction. As a consequence, the stratified tumble flows Fm,Faare allowed to exist in the combustion chamber 30 even in a compressionstroke.

Characteristic features of the first embodiment will hereinafter bedescribed successively.

A description will first be made of the configuration of the top wall 34of the piston 26. The piston 26 is provided on the top wall 34 thereofwith a raised portion 37 as illustrated in FIGS. 1, 3 and 4. On the topwall 34, a top of the raised portion 37 is located on the side of theintake openings of the intake port 46 relative to the imaginary planeFC. An inclined wall vf1 of the raised portion 37, said inclined wallvf1 being on the side of the imaginary plane FC, is formed so that theinclined wall vf1 extends smoothly in continuation from the top wall 34of the piston 26. Further, the inclined wall vf1 of the raised portion37 is also formed so that straight lines are formed parallelly betweencross-sections parallel with the imaginary plane FC and a base plane ofthe top wall 34 of the piston 26. In other words, the inclined wall vf1of the raised portion 37 is formed such that, when the tumble flowsFm,Fa change their direction to flow along the top wall 34 of the piston26 and then along the inner wall of the cylinder 24 during an intakestroke, they are kept stratified without mutual mixing.

In addition, an inclined outer wall vf2 of the raised portion 37 isconstructed such that, when the piston 26 is located in the vicinity oftop dead center during a compression stroke, the inclined outer wall vf2cooperates with the ceiling of the combustion chamber 30 to developsquishing SF to cause a small disturbance to the tumble flows Fm,Fa.

As is illustrated in FIGS. 1, 3 and 4, the inclined outer wall vf2 ofthe raised portion 37 is provided with valve recesses 39 to avoidinterference with the intake valves 58. This construction allows thepiston 26 to take a top dead center position, where a high compressionratio is available, without interference with the intake valves 58 evenif opening of the intake valves 58 is overlapped with opening of theexhaust valves 61.

It is to be noted that illustration of the partitions 21 is omitted inFIG. 3 for the convenience of description.

A description will next be made of the partitions 21 provided inside theintake ports 46A,46B described above. Each partition 21 is arranged, asillustrated in FIG. 5, with a downstream-side end portion 21B thereofextending close to the corresponding intake valve 58 in the intake port46A or 46B. Described specifically, the downstream-side end portion 21Bof each partition 21 is formed with a suitable clearance maintainedbetween the downstream-side end portion 21B and a valve head 56 of thecorresponding intake valve 58 and a valve stem 57 extending across theintake port 46A or 46B so that neither the valve head 56 nor the valvestem 57 is brought into contact with the downstream-side end portion21B. Owing to this construction, operation of each intake valve 58 isnot affected at all by its corresponding partition 21. Each partition 21is formed along a central streamline 45A of individual streamlines 45 inthe corresponding intake port 46A or 46B and also along the axis 1A or1B of the corresponding intake port 46A or 46B. As a consequence, airflows inducted through the intake port 46 are allowed to enter in a morestraightened state into the combustion chamber 30. Since the intakeports 46A,46B are substantially parallel with each other, thesepartitions 21,21 are also arranged substantially parallel with eachother.

As is depicted in FIGS. 2 and 6, an upstream-side end portion 21A andthe downstream-side end portion 21B of each partition 21 are each shapedto define an outwardly-convex, curved surface so that straightening ofinducted air can be improved. The formation of the upstream-side endportion 21A and the downstream-side end portion 21B as described aboveis not only to achieve a reduction in flow resistance by thestraightening of inducted air but also to provide an advantage in theproduction of the partitions 21. Namely, the formation of the endportions 21A,21B of each partition 21 into such an outwardly-convex,curved surface can facilitate removal of molds (cores), which correspondto the end portions 21, upon production of the intake port 46 by castingor the like, so that the casting or the like can be conducted easilywithout failure.

The arrangement of the injector 12 and a relationship between theinjector 12 and the partitions 21 will be described next with referenceto FIGS. 1, 3, 5 and 6.

The interior of each of the intake ports 46A,46B is divided into thecentral passage 4 and the side passage 5 by the corresponding partition21 as illustrated in FIG. 6. The injector 12 as the fuel injection meansis disposed, as shown in FIGS. 1, 3 and 6, on the side upstream of thebifurcation 46C of the two intake ports 46A,46B. This injector 12 isalso designed to inject fuel toward the downstream sides of the twointake ports 46A,46B in unison with each intake stroke. Incidentally,numeral 6 in FIGS. 5 and 6 is an axis of the injector 12 and alsoindicates a central line of an injection range.

Namely, as indicated by the injection axis 6 in FIGS. 5 and 6, the fuelinjected from the side of an upper wall of the intake port is inductedinto the combustion chamber 30 through the central passage 4 and,through the side passage 5, only air is inducted into the combustionchamber 30.

The flows divided into the central passage 4 and the side passage 5 ineach of the intake port 46A,46B are therefore allowed to enter in layersinto the combustion chamber 30 while being kept separated from eachother and straightened by the corresponding partition 21. Owing to theprovision of the partitions 21 arranged as described above, the inductedair flows, after penetration into the combustion chamber 30, are broughtinto such a state as separated into three layers consisting of a layerFm of an air-fuel mixture and layers Fa,Fa of air alone (i.e., threeflows in total, one passing through the central passage 4 and the othertwo through the side passages 5 arranged on opposite sides of thecentral passage 4), in other words, stratified tumble flows as shown inFIG. 6.

The diameter of each valve stem 57 and the thickness of each partition21 will next be described with reference to FIGS. 2 and 6.

As is depicted in FIGS. 2 and 6, the central line of the partition 21and the central axis of the corresponding valve stem 57 lie in the sameplane and the thickness of the partition 21 is formed smaller than thediameter of the valve stem 57. In other words, a surface 121A of thepartition 21, said surface 121A being on the side of the central passage4, is set back toward the corresponding side passage 5 from a surface ofthe valve stem 57, said surface being on the side of the central passage4.

As is shown in FIG. 6, a spray of fuel in the flow of the air-fuelmixture along the inner surface 121A of each partition 21 is thereforecaused to advance while being guided by the inner surface of thecorresponding valve stem 57 and are then directed along arrows P towardthe spark plug 11 provided centrally on the ceiling of the combustionchamber, so that the spray of fuel is caused to center around the sparkplug 11.

The configurations of cross-sections of the intake port 46 taken indirections transverse to the intake air flows will next be describedwith reference to FIGS. 7 and 8.

As is shown in FIGS. 8(a) through 8(g), the intake port 46 is formed insuch a way that upper half portions 46A-1,46B-1 gradually become widerrelative to lower half portions 46A-2,46B-2 toward the downstream side.This makes it easier for intake air flows, which have been inductedthrough the intake ports 46A,46B, to form tumble flows within thecombustion chamber 30. In the section shown in FIG. 8(e), the intakeport 46 is bifurcated into a Siamese port so that the intake ports46A,46B are formed. Further, each port presents an inverted triangularconfiguration. The inverted, substantially triangular cross-sectionalconfiguration of the intake ports 46A,46B becomes more distinct towardthe downstream side in order to further enhance the tumble flows.

By making the upper half portion 46-1 wider than the lower half portion46-2 in each section of the intake port 46, the flow velocity and flowrate through the upper half portion 46-1 in the intake port 46 aregreater than those through the lower half portion 46-2. When the intakevalves 58 have been opened, on the other hand, there are, as depicted inFIG. 7, a flow component a promoting the tumble flows Fa,Fm and anotherflow component b suppressing the tumble flows Fa,Fm. The tumble flowsFa,Fm can therefore be made still stronger by making the flow velocityand flow rate through the upper half portion of the intake port 46greater than those through the lower half portion of the intake port 46.Since the flow component a is in the same direction as the tumble flowsFa,Fm, the flow resistance of the flow component a is extremely smalland the overall flow rate can therefore be increased significantly.

As is illustrated in FIGS. 8(a) through 8(g), the partitions 21,21 areprovided in the intake port 46 along substantially the entire lengththereof. The partitions 21,21 are provided extending from a lower wall 7of the intake port 46 to an upper wall 8 of the intake port 46 so thatthe interiors of the intake ports 46A,46B are divided transversely intotwo halves. As a consequence, the intake air flows inducted through theintake ports 46A,46B are each branched into the central passage 4 andthe side passage 5.

In other words, as is depicted in FIG. 8(a), the two intake ports46A,46B are formed as a single intake passage on a most upstream side,that is, in the vicinity of a side wall 28A (see FIG. 7) of the cylinderhead 28. Immediately after that, the flow of inducted air is branchedtoward the central passage 4 and the side passages 5 by the partitions21. As is illustrated in FIGS. 8(b) through 8(d), the central passage 4is then gradually divided into two halves and on the side downstream ofthe section shown in FIG. 8(e), the inducted air flow is completelyhalved. The intake air flows divided into the two halves as describedabove are then allowed to enter the combustion chamber 30 by therespective intake valves 58.

The intake port 46 will be described in further detail with reference toFIGS. 7, 8 and 9.

The intake port 46 has a substantially straight configuration as shownin FIG. 7 so that intake air flows are directed to form tumble flowswithin the combustion chamber 30. Because of the structure of thecylinder head, on the other hand, it is impossible to make an axis ofthe intake opening, which is selectively opened or closed by each intakevalve 58, conform with the direction of an inducted air flow. Downstreamend portions of the respective intake ports 46A,46B are thereforeconnected to their corresponding intake openings via bent portionshaving a large curvature. The actual cross-sectional flow area thereforebecomes smallest at each bent portion as is clearly envisaged from FIGS.8(f) and 8(g). Coupled especially with the existence of the valve stem57, a stem guide (not shown) and the partition 21, the actualcross-sectional flow area is reduced substantially there.

To cope with this, the intake ports 46A,46B are each provided withinflated parts 13,13 dimensioned such that the inner width of the intakeport becomes greatest at the bent portion and is set greater there thanthe intake opening selectively opened or closed by the correspondingintake valve 58. This can prevent the actual cross-sectional flow areafrom being reduced at each bent portion and can assure a sufficient flowvelocity and flow rate.

Since the inflated parts are formed primarily in the upper half portions46A-1,46B-1 of the respective ports 46A,46B as is evident from FIG. 9,the flow velocity and flow rate through the upper half portions46A-1,46B-1 can be made still greater than those through the lower halfportions 46A-2,46B-2 so that the formation of the tumble flows Fa,Fm canbe achieved more effectively.

As the stratified burning internal combustion engine as the firstembodiment of the present invention is constructed as described above,the intake air flowed into the combustion chamber 30 through therespective intake ports 46A,46B during an intake stroke forms the tumbleflow Fm of the air-fuel mixture and the tumble flows Fa of air aslayers. The stratified tumble flows Fm,Fa still remain even after thepiston operation next enters a compression stroke. When the pistonhowever approaches close to top dead center during the compressionstroke, the individual tumble flows Fm,Fa are begun to be deformed. Arich air-fuel mixture however still exists around the spark plug 11within the combustion chamber 30. In this state, ignition is conductedby the spark plug 11. Subsequent combustion and expansion stroke andexhaust stroke are exactly the same as those in a conventionalstratified burning internal combustion engine.

Even when the air-fuel mixture is leaner than the stoichiometricair/fuel ratio as a whole inside the combustion chamber 30, the featuresdescribed above make it possible to operate the engine withoutimpairment to the ignition because of the existence of an air-fuelmixture containing the fuel at a concentration sufficient for ignitionin the vicinity of the spark plug 11.

In the above-described first embodiment, in particular, the top wall 34of the piston 26 is provided with the inclined wall vf1 of the raisedportion 37, whereby the tumble flows Fm,Fa are formed with greaterstrength and hence in a more complete stratified form. As a consequence,fully-stabilized ignition and combustion can be achieved even when theair/fuel ratio of the air-fuel mixture in the entirety of the combustionchamber 30 is lowered further.

By the squishing SF which the inclined outer wall vf2 of the raisedportion 37 of the piston 26 develops in cooperation with the ceiling ofthe combustion chamber in the vicinity of top dead center of acompression stroke, a small disturbance is caused to occur in theair-fuel mixture. The burning velocity after the ignition can beimproved accordingly. Since this squishing SF gives adverse effects ifit is too strong, it is important to suitably adjust the clearancebetween the inclined outer wall vf2 and the ceiling of the combustionchamber 30 when the piston assumes the top dead center. Further, theinclined outer wall vf2 of the raised portion 37 is provided with thevalve recesses 39, whereby even when opening of the intake valves 58 isoverlapped with that of the exhaust valves 61 when the piston 26 hasreached the top dead center, the inclined outer wall vf2 is preventedfrom interfering with the intake valves 58. This makes it possible toset the top dead center of the piston 26 at a higher point to provide ahigher compression ratio, whereby the combustion efficiency can beimproved.

As is shown diagrammatically in FIG. 10, it is possible to operate anengine with a leaner air-fuel mixture by providing the intake ports46A,46B with the partitions 21, respectively, and hence promoting thestratification of the air-fuel mixture. In the diagram, air/fuel ratios(A/F) are plotted along the axis of abscissas while both amounts of NOxemitted and variations of Pi (indicated mean effective pressurevariations) are plotted along axis of ordinates. Curves a,c indicatecharacteristics of an engine whose intake ports are each provided with apartition 21, whereas curves b,d represent characteristics of an enginewhich has conventional tumble flow intake ports not provided with thepartition 21. The curves a,b relate to NOx emission and the curves c,dpertain to Pi variation.

As is clearly envisaged from FIG. 10, the emission of NOx reaches a peakon a leaner side of A/F in the case of the engine provided with thepartitions 21 (see the curve a) than in the case of the engine makinguse of conventional tumble flows (see the curve b). Further, the formerengine can reduce the peak value itself of the NOx emission. Namely, thestratification of tumble flows inside the combustion chamber 30 ispromoted so that the A/F value corresponding to a peak value of NOxemission is shifted toward the leaner side than the conventional engine.

On the other hand, the curves c and d each indicates a relationshipbetween A/F and Pi variation. Here, Pi variation provides an indicationwhich makes it possible to judge the combustion stability of an engine.If the Pi variation is too high, the combustion in an engine is notstabilized, resulting in an unpleasant operation accompanied byvariations in torque. Incidentally, a reference line e in the diagramindicates a Pi variation of a stable burning limit for generallypermitting an operation without discomfort.

As is shown in the diagram, the engine provided with the partitions 21(see the curve c) can be operated at a leaner A/F ratio than the enginemaking use of conventional tumble flows (see the curve d) at the limitvalue of Pi variation for the attainment of stable combustion in eachcylinder, and can also reduce NOx emission substantially at the limitvalue of Pi variation. Namely, the diagram indicates that the engineprovided with the partitions 21 can obtain stable combustion even at aleaner A/F ratio and can also improve the A/F ratio at the stableburning limit.

The construction of the first embodiment can therefore realize an enginewhich features extremely low fuel consumption and emits substantially noNOx.

Since the thickness of each partition 21 is smaller than the diameter ofthe corresponding valve stem 57 and the central axis of the partition 21and that of the valve stem 57 lie in the same plane, the surface of thepartition 21, said surface being on the side of the associated centralpassage, is set back toward the associated side passage 5 from thesurface of the valve stem 57, said surface being on the side of thecentral passage. A spray of fuel in the flow of the air-fuel mixturewithin the central passage 4, said flow moving along the partition 21,is directed toward the spark plug 11 while being guided by the innersurface of the valve stem 57. The spray of fuel in the air-fuel mixtureis therefore caused to center around the spark plug 11, whereby theirignition can be achieved well and the lean limit can be extendedfurther.

In particular, the upper half portions 46A-1,46B-1 in the inverted,substantially triangular sections of the intake ports 46A,46B in theconstruction of the first embodiment are formed significantly large asshown in FIGS. 7 and 9. This makes it possible to maintain strong tumbleflows inside the combustion chamber 30 and to secure a sufficientflow-rate coefficient upon full throttle.

In the first embodiment, the inflated parts 13 are formed at the bentportion of each of the intake ports 46A,46B, at which bent portion theactual cross-sectional flow area becomes the smallest, and on the sidedownstream of each valve stem 57, the partition 21 which causes flowresistance is not provided. It is therefore possible to more effectivelymaintain the above-mentioned strong tumble flows inside the combustionengine 30 and the above-mentioned flow-rate coefficient upon fullthrottle.

Further, the construction that the partition 21 is not provided on theside downstream of the valve stem 57 in each of the intake ports 46A,46Bhas large merits in production as will be described hereinafter. If thepartition 21 is also provided on the side downstream of each valve stem57, it is necessary to drill the partition 21 at a part corresponding tothe valve stem 57 after casting the partition 21. The partition 21 ishowever thin, so that there is the potential problem that cracks mayoccur upon drilling. In addition, the partition 21 also exists in acantilevered fashion on the side downstream of the valve stem 57 in eachof the intake ports 46A,46B, leading to the inconvenience that theconstruction becomes no longer preferred from the standpoint ofstrength. In the first embodiment, however, the partition 21 is notpresent on the side downstream of each valve stem 57 as described above,thereby making it possible to completely avoid such inconvenience.Moreover, it has been confirmed that stratification is practicallyunaffected even when the partition 21 is not provided on the sidedownstream of each valve stem 57. The omission of the partition 21 onthe side downstream of each valve stem 57 can therefore provide suchgreat merits in production.

FIG. 11 illustrates port cross-sectional areas and average tumblingratios (tumble flow velocities/engine speeds) as a function of averageflow-rate coefficient (i.e., flow rate as a whole). In the diagram, linea shows a relationship between port cross-sectional areas and averagetumbling ratios while line b indicates a relationship between portcross-sectional areas and average flow-rate coefficients. The solidsquare () indicates the average flow-rate coefficient of an engineequipped with an intake port in which the upper half portions46A-1,46B-1 in cross-sections of intake ports 46A,46B are enlargedsufficiently.

On the other hand, the circle (∘) indicates the average tumbling ratioof an engine equipped with a conventional tumble flow intake port. Inthe case of an engine corresponding to the dot (), the upper halfportions 46A-1,46B-1 of intake ports 46A,46B have sufficiently largedimensions to provide significant port cross-sectional areas so thatboth the average tumbling ratio and the average flow-rate coefficientcan be improved as shown in the diagram.

A relationship between tumbling ratios and flow-rate coefficients cantherefore be illustrated as shown in FIG. 12, in which the triangle (Δ)corresponds to an engine making use of conventional tumble flows, thestar () to an engine in which partitions 21 are provided but thecross-sectional areas of intake ports 46A,46B are reduced because of theprovision of the partitions 21, and the solid star () to an enginehaving the construction according to the first embodiment of the presentinvention and equipped with intake ports 46A,46B whose upper halfportions 46A-1,46B-1 have been enlarged sufficiently. As is indicated byFIG. 12, the mere attachment of the partition 21 to each of the intakeports 46A,46B results in a reduction in flow-rate coefficient althoughthe stratification of inducted air flows may be promoted, leading to theinconvenience that the performance upon full throttle is lowered. Asindicated by the solid star (), both the tumbling ratio and theflow-rate coefficient can be improved by sufficiently enlarging theupper half portions 46A-1, 46B-1 of the sections of the intake ports46A,46B. In the manner described above, it is possible to compensate forthe reduction in cross-sectional area of each of the intake ports46A,46B, said reduction being caused by the provision of the partition21, thereby making it possible to maintain strong tumble flows insidethe combustion chamber 30 and also to secure the full-throttleperformance of an engine.

FIG. 13 illustrates the rotary torque and power output of an engine, inwhich curves a,c diagrammatically show characteristics of an enginehaving the construction according to the first embodiment of the presentinvention and curves b,d diagrammatically depict characteristics of anengine having a conventional intake port construction. First, each ofthe curves a,b indicates a relationship between rotary speeds andtorques of the engine. There is no substantial difference between thetwo curves, thereby indicating that the engine having the constructionaccording to the first embodiment of this invention can achieve a torquecomparative to that available from the conventional engine even when theformer engine is operated on an air-fuel mixture leaner than aconventional air/fuel ratio.

Curves c and d each illustrates an engine speedpower output relationshipof an engine. Like the torque characteristics described above, there isno substantial difference between the curve c and curve d, therebyindicating that a power output similar to that available with theconventional engine can be obtained even when operated using an air-fuelmixture leaner than that for the conventional engine.

As is shown in FIG. 13, the engine having the construction according tothe first embodiment of the present invention provides the intake ports46A,46B with an increased tumbling ratio and flow-rate coefficient and,as a result, an internal combustion engine having equivalent torque andoutput characteristics to conventional engines can be achieved.

By providing the intake port 46 with the partitions 21 and makingsufficiently large the upper half portions 46A-1,46B-1 of substantiallytriangular sections of the intake ports 46A,46B, stable combustion canbe maintained and NOx can be reduced with an air-fuel mixture leanerthan that used for conventional internal combustion engines withoutlowering both the torque and the power output from those available fromthe conventional internal combustion engines. At the same time, the fuelconsumption can also be improved.

Modifications of the configuration of the top wall of the piston willnext be described using FIGS. 14 and 15.

The engine according to the first embodiment as shown in FIGS. 1 and 3is provided with the piston 26 having the top wall 34 with the raisedportion 37 as illustrated in FIGS. 4(a) and 4(b). Instead of the piston26, a piston 26a as depicted in FIGS. 14(a) and 14(b) is adopted.

In FIGS. 14(a) and 14(b), a top wall of the piston 26a is provided witha raised portion 37a. On the top wall 34, a ridgeline 232 of the raisedportion 37a is located on the side of the intake openings of the intakeport 46 relative to the imaginary plane FC. An inclined wall vf3 of theraised portion 37a, said inclined wall vf3 being located on the side ofthe imaginary plane FC, is formed such that the top wall 34 of thepiston 26a extends as a smooth continuous wall. The inclined wall vf3has a concave configuration symmetrical with respect to a planeextending at a right angle relative to the imaginary plane FC andcontaining the axis of the cylinder, namely, a widthwise central planeof the tumble flow Fm (see FIG. 1).

In the modification of FIGS. 14(a) and 14(b), the inclined wall vf3 isrecessed as described above. Accordingly the tumble flows Fa,Fm all tendto move toward a center of the tumble flow Fm when they change theirdirections so that they flow along the top wall of the piston 26a andthen along the inner wall of the cylinder. Since the inclined wall vf3is symmetrical with respect to the widthwise central plane of the tumbleflow Fm, the stratified state of the tumble flows Fa,Fm is not deformed.

The next modification employs a piston 26b as illustrated in FIGS. 15(a)and 15(b).

A top wall 34 of the piston 26b in FIGS. 15(a) and 15(b) is providedwith a recess 35 and a raised portion 37b. On the top wall 34, aridgeline 232 of the raised portion 37b is located on the side of theintake openings of the intake port 46 relative to the imaginary planeFC. On the other hand, the recess 35 is located in the top wall 34adjacent to the raised portion 37b on the side of the imaginary planeFC. The recess 35 has a surface smoothly extending in continuation withan inclined wall vf4 of the raised portion 37b, said inclined wall vf4being located on the side of the imaginary plane FC. The inclined wallvf4 and said surface of the recess 35 are formed of a set of straightlines parallel to an imaginary line L1 which crosses at a right anglewith the axis L of the cylinder in the imaginary plane FC.

In the modification illustrated in FIGS. 15(a), and 15(b), the recess 35is provided in combination with the raised portion 37b. The stratifiedstate of the tumble flows Fa,Fm is therefore maintained more intact whenthe tumble flows Fa,Fm change their directions so that they flow alongthe top wall 34 of the piston 26b and then along the inner wall of thecylinder.

In the first embodiment and its modifications described above, theraised portions 37,37a,37b, the ridgeline 232 is positioned on the sideof the intake opening for the intake port 46. The ridgeline may howeverbe positioned on the side of the exhaust opening for the exhaust port 47so that the formation of the tumble flows Fa,Fm,Fa can be promoted by aninclined wall extending from the ridgeline toward the imaginary planeFC. As a still further alternative, two ridgelines can be provided, oneon the side of the intake opening for the intake port 46 and the otheron the side of the exhaust opening for the exhaust port 47. Theformation of the tumble flows Fa,Fm,Fa can then be promoted by twoinclined walls which extend from the respective ridgelines toward theimaginary plane FC.

In FIG. 16, characteristics of a conventional engine with pistons havinga flat top wall are indicated by curves N, those of an engine E withpistons having a top wall provided with the inclined wall vf1 shown inFIG. 1 by curves A, and those of an engine with pistons having a topwall provided with the recess 35 and the inclined wall vf4 depicted inFIGS. 15(a) and 15(b) by curves C. In the diagram, combustion stability,indicated power output and NOx reduction rate are indicated separately.During the tests, the air/fuel ratio was changed by changing the amountof air while maintaining the amount of fuel constant. A difference inindicated power output in this case shows a difference in gas mileage.

Compared with the standard type, the air/fuel ratio at the lean limitwas improved by 1 in the case of the engine E indicated by the curve Aand by 2 in the case of the engine indicated by the curve C. As aresult, NOx emission at the lean limit was reduced to 50% in the case ofthe engine E indicated by the curve A and to 16% in the case of theengine indicated by the curve C.

A modification of the partitions 21 inside the intake ports 46A,46B willnext be described with reference to FIG. 17. According to thismodification, a partition 21Q is disposed instead of the partition 21only in a substantially lower half portion of each of the intake ports46A,46B. The injector 12 is however arranged on the side upstream of thebifurcation 46C within the intake port 46 while being directeddownwardly from the upper wall of the intake port. Since fuel tends toconcentrate on the side of the lower wall of the intake port,stratification of the tumble flows Fa,Fm by the central passages 4 andthe side passages 5 is sufficiently feasible even when partitions arearranged on the side of a relatively lower wall of the intake port likethe partition 21Q.

Using FIGS. 18 to 25, a description will next be made of modificationsof the relationship between the arrangement and direction of theinjector 12 and the partitions 21.

As indicated by the axis 6 of the injector 12 in FIGS. 18 and 19, theinjector 12 injects fuel from a lower side of the intake port 46 towardobliquely upper parts of the intake ports 46A,46B on the downstreamsides of the intake ports 46A,46B. The fuel injected obliquely andupwardly is inducted into the combustion chamber 30 through the intakeport 46 and then through the central passages 4 within the intake ports46A,46B.

In FIG. 20, a partition 21C is suspended from the side of the upper wallof the intake port in place of the partition 21 of FIG. 19 so that thepartition 21C is provided only in an upper half portion of the intakeport. According to the modifications depicted in FIGS. 19 and 20,respectively, the fuel is injected toward the inner wall 8 on the upperside along the injecting axis 6 of the injector. The tumble flow Fm ofthe air-fuel mixture, said tumble flow Fm being formed in the vicinityof the spark plug 11, is richer in fuel than the tumble flows Fa on theouter sides of the tumble flow Fm. Leaner burn can therefore beestablished stably.

As is shown in FIGS. 21 and 22, the partition 21C is provided on theside of an upper half portion of each of the intake port 46 and theintake ports 46A,46B so that only the upper half portion is horizontallydivided into two sections. Further, each partition 21C is provided alonga lower edge thereof with a substantially horizontal partition 21F as anauxiliary wall so that the corresponding one of the intake port 46 andintake ports 46A,46B is vertically divided into two sections. By thepartition 21F, the interiors of the intake ports 46A,46B are dividedinto the upper half portions 46A-1,46B-1 and the lower half portions46A-2,46B-2. Further, the upper half portions 46A-1,46B-1 are eachdivided by the corresponding partition 21C into two sections, namely,into the central passage 4 (on a side of the spark plug) and the sidepassage 5 (on a side away from the spark plug). The injector 12 isarranged so that the fuel is injected to a part above the partition 21Finside the central passage 4 of each of the intake ports 46A,46B. As aresult, an outside of the tumble flow Fm of the air-fuel mixture isformed of an air-fuel mixture containing the fuel at a highconcentration. This rich air-fuel mixture is caused to center around thespark plug 11. It is therefore possible to achieve stable burning evenwith a leaner air-fuel mixture.

In FIGS. 23 through 25, an auxiliary partition 21G is provided in placeof the auxiliary partition 21F depicted in FIGS. 21 and 22. It ishowever to be noted that the injector 12 is arranged, as in the firstembodiment, on the upper wall of the intake port 46 and on the upstreamside of the bifurcation 46C. An upstream end of the partition 21Gextends close to the position of injector 12 like the verticalpartitions 21C. The horizontal partition 21G prevents the fuel, whichhas been injected through the injector 12, from spreading downwardly inthe intake port 46. Namely, on the side upstream of the bifurcation 46Cin the intake port 46, the intake port 46 is constructed such that acentral passage 4 having, for example, such a rectangular cross-sectionas in FIG. 24 is provided in an upper part of the intake port 46.Namely, the interior of the intake port 46 is divided into the centralpassage 4 and a side passage 5. On the side downstream of thebifurcation 46C, the central passage 4 is divided into two sections andis formed at upper parts of the respective intake ports 46A,46B and onthe side of a base plane 3. As a consequence, the fuel injected toward alower part of each of the intake ports 46A,46B is prevented from flowinginto the corresponding side passage 5 owing to the provision of thehorizontal partition 21G arranged in the intake ports 46A,46B. The fuelso injected hence flows into the central passage 4 in each of the upperhalf portions 46A-1,46B-1, and only air flows into the side passage 5.Since the partition 21G is provided extending from the point upstream ofthe nozzle of the injector 12 toward the downstream side, the fuel canbe allowed to flow into the central passage 4 in the upper half portionof each of the intake ports 46A,46B. An outer side of the tumble flow Fmof an air-fuel mixture is therefore formed of an air-fuel mixturecontaining the fuel at a high concentration, which is centered aroundthe spark plug 11. As a result, the air-fuel mixture is ignited andburnt as a whole without failure inside the combustion chamber, therebymaking it possible to achieve stable combustion with an air-fuel mixtureleaner than that employed conventionally.

Next, modifications of the injection by the injector 12 will bedescribed with reference to FIGS. 26(a) to 26(d).

In FIG. 26(a), fuel is injected toward the bifurcation 46C of theSiamese intake port 46. After the fuel is caused to strongly hit thebifurcation 46C, the fuel so spread is allowed to flow into the centralpassages 4 of the intake ports 46A,46B. The bifurcation 46C of theintake port 46 has a surface, which extends substantially at a rightangle relative to the injecting direction of the injector 12 so thatfuel injected through the injector 12 can strongly hit the surface andcan then spread.

FIG. 26(b) illustrates an intake port of the type that an injector 12having two fuel nozzles is employed. Two fuel flows, which have beeninjected through the respective fuel nozzles, are allowed to directlyenter central passages of respective intake ports 46A,46B. In theillustrated modification, a bifurcation 46C of the intake port, which isdesignated by numeral 46, is formed to have a curved surface so that theflow resistance to an air flow inducted has been reduced.

FIG. 26(c) shows an intake port of the type that, in order to avoidadhesion of fuel on the respective partitions 21,21, fuel is injecteddirectly into central passages 4 through the injector 12 having only onefuel nozzle. In the illustrated modification, a bifurcation 46C of theintake port, which is designated by numeral 46, is formed in an acuteangle so that the fuel can be inducted smoothly together with intakeair.

FIG. 26(d) depicts an intake port of the type that, opposite to theintake port shown in FIG. 26(c), an injector designed to inject fuelover a wide angle up to the respective partitions 21,21 is employed. Inthe illustrated modification, a bifurcation 46C of the intake port,which is identified by numeral 46, is rounded to have a curved surfacefor lower resistance as in the intake port depicted in FIG. 26(b).

FIGS. 26(a) through 26(d) show the modifications of the injection by theinjector 12. The position and axis 6 of each injector 12 are bothidentical to those in the first embodiment.

A modification of the arrangement of the valve stem 57 and thepartitions 21 will next be described with reference to FIGS. 27 to 29.

As has been described above, the partitions 21 in the first embodimentof the present invention are formed thin as shown in FIG. 6. This is tohave the inner surface 121A of each partition 21 set back toward thecorresponding side passage 5 from the inner surface of the correspondingvalve stem 57. This can bring about the advantageous effect that a sprayof fuel in an air-fuel mixture flowing along the surface 121A of eachpartition 21 are centered around the spark plug 11 in such directions asshown by P in FIG. 6.

In an arrangement depicted in FIG. 27, with a view toward obtaining asimilar advantageous effect as in the first embodiment, the inner wallof each partition 21 is set back toward the corresponding side passage 5from the inner surface of the corresponding valve stem 57 and thecentral axis itself of the partition 21 is also set back toward the sidepassage 5 from the axis of the valve stem 57.

Arrangements such as those illustrated in FIGS. 29 and 29, respectively,can also be contemplated. Partitions 121B,121C are each set backoutwardly at an upstream portion and intermediate portion from the axisof the corresponding valve stem 57. Further, surfaces (inner surfaces)122a,123a of downstream portions 122,123 of the partitions 121B,121C,said surfaces being on a side of the spark plug 11, are inclined towarda central axis of the central passage 4 so that an inducted air flow isdirected toward the spark plug 11. According to this arrangement, theinducted air flow is more smoothly directed toward the spark plug 11 tofurther promote lean burn of an engine. This arrangement is thereforeextremely effective for stratified burning engines. In the arrangementshown in FIG. 28, only the inner surfaces 122a of the partitions 121Bare bent and outer surfaces of the partitions 121B are formed flat. Inthe arrangement depicted in FIG. 29, the thickness of each partition121C is set substantially at a constant value over the entire lengththereof, and not only an inner surface 123a but also an outer surface ofeach partition 121C are formed in a bent configuration.

By setting back at least an inner surface of each partition from theinner surface of an associated valve stem in a direction away from anassociated spark plug or causing an inner surface itself of a downstreamend portion of each partition to incline toward an associated spark plugas described above, it is possible to achieve centralization of a sprayof fuel in an air-fuel mixture, which flows along the inner surface ofthe partition, toward the side of the spark plug. The degree of thiscentralization of the air-fuel mixture toward the side of the spark plugvaries depending, for example, on the extent of set-back of each innersurface and/or the setting of inclination of each inner surface, so thatthe degree of stratification in the combustion chamber can be adjusted.

A variation of the structure of the partitions, said structurecontrolling the direction of an intake air flow inducted through theintake port 46, will next be described with reference to FIG. 30.

In the first embodiment, the inner surface and outer surface of eachpartition 21 are formed substantially in parallel with each otherbecause the configuration of the partition was simplified in view of itsproduction. In view of the primary functions of the partitions 21 thatthey serve to straighten air flows inducted through the intake ports46A,46B and to prevent disturbance of the air flows at the valve stems57, it is preferred, as illustrated in FIG. 30, to form the thickness ofeach partition 21 thinner in a direction away from the correspondingvalve stem 57 toward an upstream side and further to form it as thin aspossible at the upstream end 21A. It is also preferred to form thepartition 21 in such a way that the thickness of the partition 21becomes substantially equal to the outer diameter of the valve stem 57as the partition 21 downwardly approaches the valve stem 57. Byconstructing each partition 21 as described above, each inducted airflow can smoothly enter the combustion chamber 30 without disturbance bythe partition 21 and/or the valve stem 57.

A still further modification of the intake port 46 and an intakemanifold 14 connected to the upstream end of the intake port 46 will bedescribed next with reference to FIGS. 31 through 33.

As has been described above, the upper half portions 46A-1,46B-1 of theintake ports 46A,46B are formed wider than the lower half portions46A-2,46B-2 in the first embodiment of the present invention. Byadditionally improving the configuration of the intake manifoldconnected to the upstream end of the intake port 46, still strongertumble flows Fa,Fm can be obtained in the combustion chamber 30.

In FIG. 31, numeral 14 indicates the intake manifold connected to theupstream end of the intake port 46 which is fixed on the side wall 28Aof the cylinder head 28. The cross-sectional shapes of various parts ofthe intake port 46 and intake manifold 14 are as illustrated in FIG. 32.With a view toward permitting smooth entrance of inducted air into therespective intake ports 46A,46B, in other words, with a view towardavoiding any appreciable reduction in the flow velocity of inducted air,the cross-sectional configuration of the intake manifold 14 is graduallychanged from the upstream end to the downstream end as shown in FIGS.32(a) through 32(c). At the downstream end where the intake manifold 14is connected to intake passages 14A,14B [see FIG. 32(c)], the intakemanifold 14 is formed to have substantially the same cross-sectionalconfiguration as the intake ports 46A,46B.

Owing to the provision of the two intake passages 14A,14B, the interiorof the intake manifold 14 is formed to become more flattened toward thedownstream end thereof so that, like the cross-sectional configurationof the individual intake ports 46A,46B, upper half portions 14A-1,14B-1are more widened relative to the lower half portions 14A-2,14B-2 towardthe downstream end.

The inducted air flows therefore pass through the two intake passages14A,14B inside the intake manifold 14 with their central axes 45displaced toward the upper half portions 14A-1,14B-1 and then enter thecorresponding intake ports 46A,46B. Formation of tumble flows within thecombustion chamber 30 is therefore promoted further.

Although the partitions are disposed only inside the intake port in thefirst embodiment, it is also possible, as shown in FIG. 33, to providethe intake manifold 14 with such partitions 15,15 as horizontallydividing each of the individual intake passages 14A,14B into twosections. These partitions 15 are provided extending from upper walls tolower walls of the respective intake passages 14A,14B. By the partitions15, the interiors of the intake passages 14A,14B are each divided into acentral passage 4' and a side passage 5'. The partitions 15 are providedextending close to the downstream end of the intake manifold 14, inother words, a face where the intake manifold 14 is connected to theintake ports 46A,46B. By the partitions 15, the intake manifold 14 andthe intake port 46 divide inducted air into the central passages 4,4'and the side passages 5,5'. The intake air flows branched into thecentral passages 4,4' and the side passages 5,5' are hence completelyseparated into an air-fuel mixture and air, so that the stratificationof the tumble flows Fa,Fm inside the combustion chamber 30 is enhancedfurther.

With reference to FIGS. 34 through 36, a description will next be madeof the second embodiment of the present invention as applied to anengine having plural intake ports in which no partition is arranged.

FIG. 34 illustrates the stratified burning internal combustion engineaccording to the second embodiment, which has basically the sameconstruction as the stratified burning internal combustion engine shownin FIGS. 37 and 38 except for the configuration of a top wall of apiston 26 and the configuration of intake ports 46A,46B.

As the configuration of the top wall of the piston 26, the configurationshown in FIGS. 1, 4(a) and 4(b) or that illustrated in FIGS. 15(a) and15(b) can be adopted. The cross-sectional configuration of the intakeports 46A,46B is, as illustrated in FIGS. 34 and 35, an inverted,substantially triangular configuration with upper half portions beingmore widened than lower half portions. The intake ports 46A,46B have asubstantially straight configuration as a whole and are bentsignificantly in the proximity of intake openings to the combustionchamber 30. As shown in FIG. 36, the intake ports 46A,46B are eachprovided in the upper half portion of the bent portion thereof withinflated parts 13,13 so that the intake port has a greater innerdiameter than the intake opening of the corresponding intake port.

As a result, an air-fuel mixture and air are allowed to flow into thecombustion chamber 30 from the intake port 46A and the intake port 46B,respectively, while forming tumble flows sufficient for lean burn andalso securing a sufficient intake flow rate. It is therefore possible toimprove the combustion stability, combustion efficiency and output powerover conventional lean-burn internal combustion engines.

Incidentally, the present invention can also be applied to internalcombustion engines having three or more intake valves per cylinder. Inthe case of an internal combustion engine equipped with three intakevalves per cylinder, for example, an injector is provided in such a waythat fuel can be injected toward an intake port associated with thecentral intake valve. This arrangement makes it possible to formstratified tumble flows similar to the tumble flows Fa,Fm,Fa in thefirst embodiment. By constructing the remaining elements as in the firstembodiment or in one of the modifications of the first embodiment, it ispossible to bring about similar advantageous effects to those describedabove in connection with the first embodiment and its modifications.

The embodiments and their modifications described above are eachconstructed to form the tumble flow Fm of an air-fuel mixture and thetumble flows Fa of air inside the combustion chamber 30. The presentinvention is however not limited to such embodiments. For example, it ispossible to construct a stratified burning internal combustion engine insuch a manner that fuel is also supplied to the tumble flows Fa of airto form, instead of the tumble flow Fa, tumble flows having a smallerair/fuel ratio than the tumble flow Fm.

In each of the embodiments described above, the present invention wasapplied to a stratified burning internal combustion engine in which thetumble flows Fa,Fm are formed in a stratified form in the combustionchamber 30. It is however to be noted that the present invention canalso be applied to conventional, that is, non-stratified burninginternal combustion engines. Where each intake port in a conventionalinternal combustion engine is bent at a large curvature on a sideimmediately upstream of a corresponding opening to a combustion chamberdue to the structure of a cylinder head or with a view to forming tumbleflows to agitate an air-fuel mixture in the combustion chamber, eachintake port can be provided at the bent port portion thereof with aninflated part having an inner diameter greater than the opening. Thiscan provide intake air in a sufficient amount, thereby making itpossible to enhance the tumble flows and/or to increase the maximumintake air quantity.

We claim:
 1. An internal combustion engine comprising:a combustion chamber defined by an inner wall of a cylinder, a top wall of a piston fitted in the cylinder and a lower wall of a cylinder head, two intake ports disposed in the cylinder head on one side of an imaginary plane, which contains an axis of the cylinder, and having intake openings selectively opened or closed by corresponding intake valves, whereby air inducted through the intake ports flows from the intake openings toward an opposite side of the imaginary plane along the lower wall of the cylinder head to form mutually-parallel tumble flows in the same direction within substantially the entirety of the combustion chamber, a longitudinal partition dividing at least one of the intake ports into plural passages, a spark plug disposed on an inner wall of the combustion chamber at a position corresponding to at least one of the passages, and fuel feed means for feeding fuel into said at least one intake port, said at least one intake port corresponding to the position of the spark plug, whereby stratified tumble flows are formed in the combustion chamber during an intake stroke, wherein each of the two intake ports has a guide port portion for directing intake air to be inducted into the combustion chamber and a bent port portion connecting a downstream end of the guide port portion and the corresponding intake opening, and the bent port portion is provided with an inflated part having a larger inner diameter than the inner wall of the corresponding intake opening.
 2. The internal combustion engine of claim 1, wherein each intake ports has a substantially greater width in an upper portion thereof than in a lower portion thereof in a cross-section taken at a right angle relative to flow lines of air inducted through the intake port so that a central axis of a flow of the air inducted through the intake ports is offset toward the upper portion.
 3. The internal combustion engine of claim 2, wherein the inflated part has been formed by further widening the upper portion in the bent port portion of the intake ports.
 4. The internal combustion engine of claim 2, wherein each intake ports has an inverted, substantially triangular configuration in a cross-section taken at a right angle relative to flow lines of air inducted through the intake port.
 5. An internal combustion engine, comprising:a combustion chamber defined by an inner wall of a cylinder, a top wall of a piston fitted in the cylinder and a lower wall of a cylinder head, and an intake port disposed in the lower wall of the cylinder head and having an intake opening selectively opened or closed by an intake valve, said intake port having in the vicinity of the intake opening a bent port portion bent at a greater curvature than a port portion on a side upstream of the bent port portion, wherein the bent port portion in the vicinity of the intake opening is provided with an inflated part having a larger diameter than the inner wall of the intake opening, the intake opening of the intake port being arranged on one side of an imaginary plane containing an axis of the cylinder, the intake port having a substantially straight guide port portion on the side upstream of the bent portion for directing an intake airflow so that inducted air flows from the intake opening toward an opposite side of the imaginary plane, whereby a tumble flow is formed in the combustion chamber, the intake port having a substantially greater width in an upper portion thereof than in a lower portion thereof in a cross-section taken at a right angle relative to flow lines of air inducted through the intake port so that a central axis of a flow of the air inducted through the intake port is offset toward the upper portion.
 6. The internal combustion engine of claim 5, wherein the inflated part has been formed by further widening the upper portion in the bent port portion of the intake port.
 7. An internal combustion engine of claim 5, wherein the intake port has an inverted, substantially triangular configuration in a cross-section taken at a right angle relative to flow lines of air inducted through the intake port.
 8. An internal combustion engine, comprising:a combustion chamber defined by an inner wall of a cylinder, a top wall of a piston fitted in the cylinder and a lower wall of a cylinder head, plural intake ports disposed in the cylinder head on one side of an imaginary plane which contains an axis of the cylinder, and having intake openings selectively opened or closed by corresponding intake valves, whereby air inducted through the intake ports flows from the intake openings toward an opposite side of the imaginary plane along the lower wall of the cylinder head to form mutually-parallel tumble flows in the same direction within substantially the entirety of the combustion chamber, a spark plug disposed on an inner wall of the combustion chamber at a position corresponding to a flow of air inducted through one of the intake ports, and fuel feed means for feeding fuel into said one of the intake ports, said one intake port corresponding to the position of the spark plug, whereby stratified tumble flows are formed in the combustion chamber during an intake stroke, wherein each of the plural intake ports has a guide port portion for directing intake air to be inducted into the combustion chamber and a bent port portion connecting a downstream end of the guide port portion and the corresponding intake opening, the bent port portion being provided with an inflated part having a larger diameter than the inner wall of the corresponding intake opening, each intake port having a substantially greater width in an upper portion thereof than in a lower portion thereof in a cross-section taken at a right angle relative to flow lines of air inducted through the intake port so that a central axis of a flow of the air inducted through the intake port is offset toward the upper portion.
 9. The internal combustion engine of claim 8, wherein the inflated part has been formed by further widening the upper portion in the bent port portion of the intake port.
 10. An internal combustion engine of claim 8, wherein each intake port has an inverted, substantially triangular configuration in a cross-section taken at a right angle relative to flow lines of air inducted through the intake port. 